The following disclosure relates to cochlear stimulation systems for the treatment of hearing loss and, more particularly, to a method for optimizing pitch allocation using a harmonics-based tuner for aligning the band pass filters associated with an electrode as implemented in a cochlear stimulation system.
Generally, there are two types of hearing loss: conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss typically may be treated with the use of a hearing aid system, which amplifies sound so that acoustic information can reach the cochlea and the hair cells, or through surgical procedures. Hearing aids, however, are not effective for treating sensorineural hearing loss, no matter how loud the acoustic information is amplified, given the hair cells in the cochlea are either absent or destroyed.
Sensorineural hearing loss occurs when the hair cells in the cochlea, which are needed to transduce acoustic signals into auditory nerve impulses, are either absent or destroyed. Sensorineural hearing loss typically may be treated with a cochlear stimulation system, such as the systems described in U.S. Pat. Nos. 5,938,691 and 6,219,580, each of which is incorporated herein by reference. These cochlear stimulation systems produce sensations of sound in patients with sensorineural hearing loss by direct electrical stimulation of the ganglia of the auditory nerve cells. These systems bypass the defective cochlea hair cells that normally transduce acoustic energy into electrical activity in such nerve cells, leading to perception of sound in the patient's brain.
Cochlear stimulation systems typically include an electrode array, an implantable cochlear stimulator (“ICS”), an externally wearable signal processor (or speech processor, portions of which can be implanted) and a microphone. The speech processor generally employs a headpiece that holds the microphone to be positioned adjacent to the patient's ear. In operation, the electrical stimulation applied to the ganglia is derived from acoustic signals received by the microphone and transformed into control data by the speech processor that is programmed during a fitting process to meet the particular requirements of each patient. The speech processor transmits the control data to the ICS, which uses the control data to selectively generate electrical stimuli and to apply the electrical stimuli to one or more cochlea stimulating channels, each associated with an individual electrode or a pair or group of electrodes within or on the electrode array, which is typically surgically inserted into the patient's cochlea.
Within the cochlea, there are two main cues that convey “pitch” (frequency) information to the patient. They are (1) the place or location of stimulation along the length of a cochlear duct and (2) the temporal structure of the stimulating waveform. Because each place along the cochlea corresponds to a specific perceived sound frequency, the relationship between the cochlear place and perceived sound frequency is typically different for every individual as no two cochleas are alike and the nerve wiring between the cochlea and to the brain is different for every individual. In the cochlea, received sound frequencies are mapped to a “place” in the cochlea, generally from high to low sound frequencies from the basilar to apical direction.
At present, many patients fitted with a cochlear stimulation system find it difficult to enjoy music generally because the mapping of the electrode array in a cochlear duct to the perceived audio frequencies is not correct. Correctly mapping an electrode array in a cochlear duct to the perceived audio frequencies is complicated by differences in a patient's anatomy as mentioned above. Often times, when the electrode array is surgically inserted into a patient's cochlea, the final implanted position of the electrode array is misaligned with the proper place along the patient's cochlea. Moreover, the nuances of the electric field propagation at each electrode contact in the electrode array tends to be variable. Both the misalignment of the electrode contacts and variability of the electric field propagation leads to an arbitrariness to a mapping scheme between the electrode contact and the perceived sound frequency—i.e., the perceived sound frequencies are not the same as the correct received sound frequencies. Conventional fitting programs that process delivery of certain received sound frequencies through a selected electrode contract or electrode contacts typically do not compensate for this misalignment and variableness.
U.S. Pat. No. 7,702,396, incorporated herein by reference, attempts to overcome these problems by providing an improved fitting tool to better convey pitch information to a user of a cochlear implant. The disclosed methods and systems provide a fitting routine using melodies to help properly map specific electrodes and/or “places” on the cochlear to corresponding perceived audio frequencies. The use of melodies, however, for tuning or mapping tends to be problematic for those users having poor auditory memory or musical training.